In the process for manufacturing the semiconductor, a trenched polysilicon structure is often used to increase the effective area of the capacitor, especially when the semiconductor is a miniaturized dynamic random access memory (DRAM). Because of the tendency of demanding the smaller size of semiconductor, different kinds of methods must be employed to increase its effective area so that the characteristic of the semiconductor will not be worsen as a result of the restriction on its size. In the conventional method, the trenched polysilicon structure is formed through the amorphous silicon deposition followed by an annealing process. Due to the relatively narrow temperature range (570.about.580.degree. C.) for the deposition in this method, it is very hard to control the environment factors to maintain a proper temperature for the reaction system of the method.